I have a custom master page called custom.master which I have tweaked to enable a drop down 'Mega Menu' placed underneath the titlebar. I have gotten it working in my site (which is not the root site, it is one level under). I have 5 different sub sites branching out from my site which I want to inherit custom.master.
I have searched but always get the same answer everytime. In the Master Page settings I cannot see my custom.master page! Only v4.master and nightandday.master when I drop down the arrow. I have set custom.master as default in my site by right clicking it in Sharepoint designer. I have checked that custom.master is a major version and published.
It also may be of note when I go into the master page settings I get two warnings up the top: "The site master page setting currently applied to this site is invalid. Please select a new master page and apply it" and "The system master page setting currently applied to this site is invalid. Please select a new master page and apply it."